The present invention relates to apparatus for treating webs consisting of paper, imitation cork or other flexible material, particularly for reducing or completely eliminating localized stresses in and/or for reducing or eliminating differences in the length of lengthwise extending portions of a web which is stored in the form of a bobbin and is used in the manufacture of smokers' products.
It is known to utilize in tobacco processing machines a stationary curling bar which is a device for reducing (and preferably eliminating) localized stresses as well as for reducing or eliminating differences in the length of lengthwise extending strip-shaped portions of a web of paper, imitation cork, reconstituted tobacco or the like. As a rule, the curling bar resembles a blade fixedly mounted in a support and having an elongated edge-like portion which bears against one side of the running web and imparts to the web a tendency to curl. Such treatment of the web by contact with the edge-like portion of the curling bar is intended to eliminate or reduce localized stresses in the material of the web as well as to equalize the length of lengthwise extending portions of the web. The treatment with a curling bar is especially desirable in connection with the making of so-called uniting bands which are used to connect filter rod sections with plain cigarettes, cigarillos or cigars to form filter cigarettes, cigarillos or cigars of unit length or multiple unit length. Uniting bands which are used in a filter cigarette making machine normally consist of artificial cork which is a paper base material powdered on the outside to imitate cork and coated with adhesive at the inside prior to draping it around a filter rod section and around one or more plain cigarettes of unit length. Webs of artificial cork are stored in the form of bobbins which are obtained by subdividing an elongated cylindrical roll of convoluted sheet material into slices of desired axial length. At the present time, sheets of artificial cork have a width of up to and in excess of two yards. Such sheets are convoluted to form long rolls which are thereupon severed in planes at right angles to their axes to yield a plurality of bobbins ready for use in a filter cigarette making machine. In such machine, the web is withdrawn from the bobbin by one or more driven rolls and its leader adheres to the peripheral surface of a suction wheel cooperating with a rotary knife to sever the leader at regular intervals and to thus furnish a succession of uniting bands. During travel from the bobbin to the suction drum, the web is flexed by the curling bar and thereupon passes along a paster which coats one of its sides with a suitable adhesive. The uniting bands are attached to successive groups of filter rod sections and plain cigarettes and are thereupon rolled around such groups to form therewith filter cigarettes of unit length or multiple unit length.
The curling bar performs two important functions namely to eliminate localized stresses in the material of the web and to equalize the length of lengthwise extending portions of the web. Localized stresses develop during the making of sheets which are thereupon coiled and severed to yield discrete bobbins. Such severing also causes changes in the length of lengthwise extending portions of the web. As a rule, at least one marginal portion of the web is longer than the other marginal portion, or both marginal portions are longer than the median portion. In the absence of curling, uniting bands which are obtained by subdividing the web cannot be readily coiled around filter rod sections and plain cigarettes. Also, when coiled, the uniting bands tend to open up so that many filter cigarettes exhibit leaks which are detected by testing apparatus and the respective cigarettes segregated from satisfactory cigarettes.
Conventional curling bars can eliminate some localized stresses and/or differences in the length of lengthwise extending portions of webs. However, their action is not entirely satisfactory and, moreover, they often cause the web to break which invariably entails substantial losses in output. The breakage of webs is attributable to the fact that, when the web travels along the edge portion of a fixedly mounted curling bar, its resistance to tearing is greatly reduced in the region where the one or both marginal portions are longer than the median portion because the pressure which the running web exerts against the curling bar or vice versa must be taken up exclusively by the relatively narrow median portion of the web.
The situation is similar when a running web of relatively stiff paper or the like is converted into the wrapper of a continuous filter rod or when a web of reconstituted tobacco or the like is converted into helical wrappers of cigars.